This invention relates, in general, to isolator circuits, and more particularly to isolators for coupling a circuit to a switch.
In general, an isolator is used to electrically isolate one circuit from another. A common form of isolator is an optical coupler (opto-coupler). The optical coupler typically has a light emitting diode (LED) for emitting light to a detector diode which senses the emitted light and provides a current signal. The light emitting diode optically couples to the detector diode. For example, a control circuit operating at a low voltage is coupled to the secondary side of the opto-coupler where the light emitting diode resides. The control circuit enables a primary side circuit (operating at hazardous voltages) coupled to the primary side of the opto-coupler where the detector diode resides. This allows the primary side circuit to be controlled through the opto-coupler without the control circuit being exposed to the hazardous voltage.
In the example described above, both the control circuit and the primary side circuit are powered by their own independent power supplies. Power must be supplied to the light emitting diode of the opto-coupler. There are cases, such as remote switching when a power supply to the secondary side of the isolator is not available or convenient. Isolated remote switching is simply a switch isolated from a circuit through an isolator. It would be of great benefit if an isolator could be provided that need not be powered on the secondary side of the isolator but is electrically isolated from the circuit.